In semiconductor devices such as semiconductor laser devices and high performance MPU's (microprocessing units) used in optical communications and the like, the issue of how to efficiently dissipate the heat from the devices is crucial for preventing malfunctions.
In recent years, advances in semiconductor device technologies have resulted in higher outputs, higher speeds and higher integration of devices, thus requiring even greater heat dissipation. This has resulted in demands for higher thermal conductivity in heat dissipating components such as heat sinks, so that copper (Cu), having a high thermal conductivity of 390 W/mK, has been used.
On the other hand, the higher outputs required of individual semiconductor devices has caused them to become larger in size, thereby raising the problem of mismatched thermal expansion between semiconductor devices and heat sinks used for heat dissipation. This problem has led to a demand for the development of a heat sink material having both high thermal conductivity and a thermal expansion coefficient matching with that of semiconductor devices. Composites of metals and ceramics, such as a composite of aluminum (Al) and silicon carbide (SiC), have been proposed (Patent Document 1) as such materials.
However, with Al—SiC type composite materials, no matter how the conditions are optimized, the thermal conductivity will never be more than 300 W/mK, so the development of a heat sink material having even higher thermal conductivity, equal to or greater than the thermal conductivity of copper, is desired. As such a material, a metal-diamond composite, combining the high thermal conductivity of diamond with the high coefficient of thermal expansion of metals and thus having a high thermal conductivity and a coefficient of thermal expansion close to that of semiconductor device materials, has been proposed (Patent Document 2).
Additionally, in Patent Document 3, a β-type SiC layer is formed on a surface having diamond grains, so as to suppress the formation of metal carbides of low thermal conductivity during the compositing process and improve the wettability for molten metals, thereby improving the thermal conductivity of the resulting metal-diamond composite material.
Furthermore, since diamond is an extremely hard material, the metal-diamond composite materials obtained by compositing with metals are similarly very hard, and they are difficult to work. For this reason, metal-diamond composite materials are usually not easily workable with diamond machine tools, so when wishing to use metal-diamond composites in heat sinks which are small and come in a variety of shapes, the problem is how to shape the material at a low cost. Since metal-ceramic composite materials are capable of conducting electricity, processing methods using electrical discharge processing have been considered as a potential solution.    Patent Document 1: JPH9-157773A    Patent Document 2: JP2000-303126    Patent Document 3: JP 2007-518875T